This invention relates to a novel poly(urethane amideimide), or urethane-amide-imide copolymer, composition, which has excellent mechanical strength and heat resistance. More particularly, this invention relates to a heat-resistant linear copolymer composition containing urethane, amide and imide groups in the polymer backbone thereof for use as a wire coating varnish and film material, and the method of making the same.
Polymeric materials have been widely used in the field of electric insulation. Those polymers that have been commonly used in these applications include polyimide, polyamideimide, polyesterimide, polyester, polyurethane, and others. The aforementioned polymers are also useful as adhesives, film insulation material, water sealants, and as packing material for integrated circuits. Polyurethanes are known to have good mechanical properties (i.e., high tensile strength), electric insulating characteristics (i.e., ability to withstand electric overload) and fabricability. Furthermore, because of its relatively low manufacturing cost, the potential market of polyurethane can be quite significant. However, polyurethanes suffer from their lack of heat resistance, therefore, their long-term application is limited to relatively low temperature environment. Many studies have been attempted to improve the heat resistance of polyurethanes.
In the attempts to improve the heat resistance of polyurethane, the following approaches are most commonly employed: (1) using a blending approach to blend heat-resistant material, such as polyimide, polyesterimide, and/or polyamideimide, into the polyurethane matrix to improve the heat resistance thereof; (2) using a blocking agent approach to protect the diisocyanate group in the prepolymer of polyurethane before reacting with polyfunctional alcohols to form a polyurethane copolymer with improved heat resistance. In the first approach, long-term compatibility is a problem; phase separation often occurs in the polyurethane blends resulting in serious degradation of the physical properties thereof. The second approach involves a complicated manufacturing process, and the final product, when hardens, often contains gas bubbles formed therein which adversely affect the product quality and limit its potential applicability.